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Interesting marks on air filter - 5/6th gen


Stray

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Here’s a curiosity I thought may intrigue VFR owners. 

 

Bought a 6th gen airbox off fleabay and it came with a Pipercriss foam filter. Looks like it was installed only a short time ago as it’s not too filthy. Anyway, I found the dirt marks intriguing as they appear to be quite localised over the velocity stacks. 

 

0ACC2027-F883-4A29-AAA5-ABD29D13E10A.thumb.jpeg.2db0b71001b9a874e0aee6e384253e75.jpeg

 

Then, when looking a bit more closely I realised there were other marks too. 

 

Here’s a pic showing filter next to lid. Bottom section of airbox is a mirror of the filter. 

 

B48A1AC6-CE91-4832-A371-2CCFCA1490AF.thumb.jpeg.a122d154f377e4b7717574327400d02e.jpeg

 

Front of airbox is down and rear is up. 

 

There seems to be a concentration of dirt near the flapper and another spot near the PAIR spigot. Nothing near the snorkel though?!

 

I can see the snorkel is still attached to the lid but the PO had clearly done the “flapper mod” as there was some insulation tape over the nozzle of the actuator thingy. 

 

What i cant tell is if PO had done the PAIR removal and block-off mod. There is clearly air going in at the PAIR spigot but it could be from either normal PAIR functioning or faulty block-off after removal. 

 

Strange thing is the PAIR spigot is BELOW the air filter so how did the filter get dirty at that point? Air coming into the spigot should have flowed nowhere near the filter and straight into the velocity stack. 

 

Also, why so much filth near the flapper and none near snorkel? Makes no sense as flapper is open only half the time whereas snorkel is open always. 

 

Thought: could it be dirty air flowing BACKWARDS, out of the engine and toward the filter? Could it be stains from combustion gasses that escaped from a worn intake that’s no longer airtight? 

 

I’m posting purely for intrigue. Maybe someone who understands airboxes can enlighten? 

 

HAPPY NEW YEAR! 

 

Stray

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looking at your picture (just my opinion/perspective) it seems that the dark marks correspond to the locations of the velocity stacks much more than they do to the intake snorkel and flapper combination.  And, yes, in my experience the filter is always dirty near the PAIR.

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If you get a dirty spot near the PAIR outlet that would suggest the reed valves at the cylinder head are not sealing, and allowing some exhaust gas to make it back to the airbox. The PAIR should only supply air to the exhaust, not receive any.

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On 31/12/2017 at 11:55 PM, Marooncobra said:

That is not the PAIR inlet but the oil breather recirculation inlet. The pair inlet is at the same end of the air box but the other side.

Are you sure?

 

Remember the air filter is flipped in comparison to the air box lower in the pic. So the stain on the top right of the filter corresponds to the top left of the air box lower. 

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On 31/12/2017 at 10:54 PM, GreginDenver said:

looking at your picture (just my opinion/perspective) it seems that the dark marks correspond to the locations of the velocity stacks much more than they do to the intake snorkel and flapper combination.  And, yes, in my experience the filter is always dirty near the PAIR.

Greg, I agree if you look st the top two stains - they are pinpoints of where the velocity stacks sit. 

 

But that great big big stain at the bottom tells a different story, otherwise there would only be two pinpoint stains there too. 

 

Also, how can we explain that third little stain on top right? Can’t be a velocity stack. 

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On 31/12/2017 at 11:45 PM, Terry said:

If you get a dirty spot near the PAIR outlet that would suggest the reed valves at the cylinder head are not sealing, and allowing some exhaust gas to make it back to the airbox. The PAIR should only supply air to the exhaust, not receive any.

Terry, I  agree with you. Something is amis on the donor bike. I’m hoping it’s not something all our bikes suffer with. 

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1 hour ago, Stray said:

Are you sure?

 

Remember the air filter is flipped in comparison to the air box lower in the pic. So the stain on the top right of the filter corresponds to the top left of the air box lower. 

Yes, 

 

if if you look at the air box bottom half, with the four holes for the velocity stacks, the oil breather opening is on the top left, in front of the MAP sensor, and looks like a half moon. The filter black oil stain corresponds to this location.

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